James Lee, the bomb-laden gunman who was killed by police in the lobby of the Discovery Channel, was once convicted and imprisoned for smuggling illegal immigrants into the country from Mexico.

The revelation that Lee had once smuggled illegals contrasts sharply with a hate-filled manifesto he left behind in which he describes illegal immigrants as "disgusting filth" and their children as "anchor baby filth."

As his smuggling history came to light, new details emerged about Lee's deadly confrontation with police on Wednesday.

"My sense from listening to him was that he had no intention of leaving alive," Manger said.

Police also said today that the gun he used to menace his hostages and police was a starter's pistol. In addition, authorities discovered and safely detonated more four explosive devices found inside Lee's home.

Documents in the 2003 people smuggling case highlight Lee's descent into isolation and despair.

According to a copy of his plea agreement and a jailhouse confession written to the judge on the eve of his sentencing, Lee was choked and robbed in a Tijuana, Mexico, hotel room, before his assailants induced him to become a human trafficker.

"There I was in a Tijuana hotel being further subjected to more of life's brutality. There I was just being finished being choked and robbed. Then they offered me work. I had nothing left so I tried it. I started to smuggle people for them," Lee wrote Judge Barry Ted Moskowitz in August 2003.

Police Set Off Explosives at Discovery Channel Headquarters

He quickly came to like the job.

"For one brief moment in my whole worthless life I felt good about myself. I felt like I was really helping people. I have never saved a person's life, but it felt the same as I imagine it would have felt… For once my life seemed to actually benefit the lives of others," he wrote to the judge.

Lee was arrested trying to smuggle a woman in a concealed compartment of his car through the San Ysidro border crossing in southern California and was sentenced to 18 months in prison, according to court documents. He later said he was ashamed of his people smuggling.

The jailhouse letter also offers eerie foresight into Lee, who described his life as "a living, breathing nightmare."

"When I get out of prison, I undoubtedly will have the same personality traits as I had before. I wish I could point a finger at someone or something and magically be someone else.... I don't know if my life will end with a happy ending, but all I ask is for an ending that is not in prison," he wrote.

James Lee's Family Says He Was Estranged

Lee's sister-in-law Tuonglan Lee confirmed to ABC News.com that Lee had been arrested and sentenced in 2003 for human smuggling.

The documents do not mention how many people Lee smuggled across the border, but Tuognlan Lee said her family was contacted at the time by the FBI and told "it was more than one."

Lee had been estranged from his family since 2002, according to Tuonglan. "We last spoke to him in 2002. The next time we heard about him was in 2003 when we heard about the Mexico incident. Then we had no news until he was arrested again in 2008 and then of course the news yesterday. We always wonder what he was doing."

Lee was arrested in 2008 for disorderly conduct during a protest outside of Discovery Channel headquarters.

Tuonglan Lee said his mental state diminished over time. "Two people close to him died in 2002, and after their passing he became angry and very emotional. He had a normal relationship with people before 2002, but after that he was completely different."

Lee's brother told ABC News that Lee was likely seeking to be killed by the police.

"It was definitely out of character," Aaron Lee said. "I thought it was insanity. I was sad to know that he was shot and killed, but that's what he probably wanted."

Lee, 43, was killed Wednesday as he brandished a gun and wore an explosive device in the lobby of the Discovery Channel headquarters where he had taken three people hostage.

"Any time that police officers use deadly force, it's to save a life... In this situation the hostages -- who were tremendously courageous throughout this incident -- were in grave danger," Montgomery County Police Chief J. Thomas Manger told "Good Morning America."

Manger said that SWAT officers had been able to sneak "very close" to Lee without alerting him, close enough to hear a disconcerting "pop."

"SWAT officers heard a shout, they heard a pop. They were unclear if that was a gunshot or if it was the suspect detonating a device," Manger said. "The officers immediately confronted the suspect. He had a gun out and he was shot at that point."

After Lee was killed and all the hostages safely evacuated, police found several makeshift explosive devices both strapped to Lee's body and in a box and bag that he had brought into the building. In addition, police recovered a second handgun and a ski mask.

"Attached to propane cylinders, he had pipes that contained shotgun shells. In addition he had a couple of pipe bombs strapped to it. They appeared to have some sort of firework type material inside of them," Manger said.

One of the devices reportedly went off when Lee was shot. The rest were detonated overnight by police who have since swept the building and found no other explosives.

James Lee Warned That He Was Rigged to Explode

Lee warned that he was wired to explode. Remarkably, the gunman picked up the phone when a reporter for NBC News called the lobby. When asked if he had a gun, Lee responded, "I have a gun and I have a bomb. I have several bombs strapped to my body ready to go off."

It's believed Lee invaded the building as the final act in a longstanding protest against the Discovery Channel for promoting what he called an anti-environmental message.

In a rambling manifesto on Lee's website, believed to have been written by Lee, the writer rails against "disgusting human babies," "parasitic infants," and says people should "disassemble civilization." The manifesto also calls on Discovery to "broadcast to the world their commitment to save the planet."

For at least two years Lee called for protests against the company and was arrested and found guilty of disorderly conduct for a protest outside of Discovery's Maryland headquarters in 2008. Due to these past actions, security at the Discovery Channel offices knew who Lee was and "immediately identified" him during this incident, Manger said.

The drama began when workers in the building got a bulletin from the building's security at around 1 p.m.

"We have reason to believe there is an armed gunman at One Discovery Place. All employees should seek protection in a locked office on their respective floors immediately," read an email sent to employees and read over the public address system.

"There's a guy with a gun in the lobby. Police are swarming in -- assault rifles and all," one producer told ABCNews.com via instant message.

Employees at the building were told to take cover in locked offices and police have sent SWAT teams to the area to seal off nearby roads.The FBI and agents from ATF, including explosives experts, also rushed to the building.

Many were trapped inside the suburban headquarters.

"Friends, I am in work closet with workers here. There is a shooter here at Discovery. I am ok," read a text from one Discovery employee.

Another employee said the Lee had taken a hostage. "The police are trying to get the situation under control!INSANE!" read the email to ABCNews.

James Lee's Angry and Rambling Manifesto

Some employees were initially sent to higher floors and later evacuated, police said. Witnesses on the scene said another group of employees left the building around 1:44 p.m.

The building has a daycare center, which was evacuated with infants rolled through the street in cribs.

"Crazy to see the babies coming out of childcare center piled into rolling cribs into the McD's across the street, a safe zone," said a witness Wednesday via email.

The building, which houses the offices of Discovery Channel and its sibling networks including Animal Planet, is located just outside Washington DC.

Lee operated the Web site savetheplanetprotest.com and was arrested in 2008 following a demonstration held at Discovery's headquarters. Lee was found guilty of disorderly conduct.

According to a post on his Web site, Lee said he was thrown "in the nut house" for four days following his arrest.

Lee has been demanding a boycott of Discovery Channel since at least 2008.

On his website, Lee posted a rambling manifesto under the title "My Demands," which espouses a far-radical environmentalist and misinthropic philosophy and calls on the channel to cease programming about giving birth, war and weapons.

"The planet," he wrote, "does not need humans."

The document, which appears to have been created on July 17, is interspersed with references to esoteric philosophers, childish language, misspellings, and capital letters.

Lee writes that the channel should cease its current programming and replace it with a game show about reducing the global population.

The channel, he wrote, should produce a program about "how people can live WITHOUT giving birth to more filthy human children since those new additions continue pollution and are pollution."

"The world needs TV shows that DEVELOP solutions to the problems that humans are causing, not stupify the people into destroying the world. Not encouraging them to breed more environmentally harmful humans," he wrote.

"Saving the environment and the remaning [sic] species diversity of the planet is now your mindset. Nothing is more important than saving them. The Lions, Tigers, Giraffes, Elephants, Froggies, Turtles, Apes, Raccoons, Beetles, Ants, Sharks, Bears, and, of course, the Squirrels. . . The humans? The planet does not need humans," he wrote.

-- This embed didnt make it to copy for story id = 11541307.
-- This embed didnt make it to copy for story id = 11541307.
-- This embed didnt make it to copy for story id = 11541307.
-- This embed didnt make it to copy for story id = 11541307.
-- This embed didnt make it to copy for story id = 11541307.
-- This embed didnt make it to copy for story id = 11541307.
-- This embed didnt make it to copy for story id = 11541307.